[TowerTalk] The tower base is poured BUT...

[Jim Lux]

Sure, there are truck mounted augers that can bore a lot deeper than 25'...
The cave in issue is mostly for the upper layers of soil. Once you get down
very deep, the soil tends to be more like "soft rock" and is fine for
drilling... The other thing to think about is that the auger operator has
drilled hundreds of holes and are well  aware of what's feasible and what's
not in a given area, and what the specific techniques needed are.

 I'm assuming that the engineer is local and familiar with what works; after
all, that's why you hire a local engineer. Partly, also, this is  why each
state requires your plans to be stamped by an engineer licensed to practice
in that state. Although, I concede that in a large state like CA, I don't
know that an engineer practicing in far northeastern counties would
necessarily be familiar with the peculiarities of my local area in SoCal,
but then, it wouldn't be ethical (or legal) for the distant engineer to do
the work without knowledge of local conditions.  The bulletin I get from the
Board of Professional Engineers and Land Surveyors has lots of enforcement
actions listed for just this kind of thing ("mail-order wet stamps").. I
will also admit that some of the licensure requirements seem to be  purely
for protectionism, dressed up in a "public safety" cloak.

As a practical matter, a long cylinder of reinforced concrete looks like
just the kind of structure you'd want to resist the turning forces from wind
or seismic activity on a tall tower.  Distributes the loads over a very
large area of soil, and deep into undisturbed soil, which is going to be
structurally stronger than the surface soil. A 2 foot diameter bar of
reinforced concrete is going to be quite strong (I'll bet it could support
it's own weight if it were cantelievered, certainly as a span between two
supports).

----- Original Message -----
From: "Jerry Keller" <k3bz at arrl.net>
To: "David Giuliani" <David at Giuliani.org>; <towertalk at contesting.com>
Sent: Sunday, October 05, 2003 10:20 AM
Subject: Re: [TowerTalk] The tower base is poured BUT...


OK, maybe my ignorance is showing, but does anyone else think it a bit
preposterous for an engineer to recommend digging a 25 foot deep hole for a
tower base? If the soil content would allow augering a 25 foot deep hole
only 2 feet in diameter, wouldn't it cave in long before it got that deep?
Are there even 2 foot diameter truck-mounted augers available 25 feet long?
There's something about this idea that just seems wrong... but then I'm no
engineer. Any thoughts?  Jerry K3BZ
  ----- Original Message -----
  From: David Giuliani
  To: towertalk at contesting.com
  Sent: Sunday, October 05, 2003 12:23 PM
  Subject: RE: [TowerTalk] The tower base is poured BUT...



  The more I read about this, the more I'm liking my emerging plan to dig a
  hole with a truck mounted auger rig -- no forms, no backfilling,
relatively
  small diameter surface.  We're looking at a 2' diameter hole, 25' deep.
  Relatively simple rebar for the lower 80%.  Requires <3 cubic yards of
  concrete. See "deep base for MA-550" for this thread.

  David Giuliani,